A fluorescent antibody technique was developed for the determination of the capsular‐type of strains of Staphylococcus aureus. It compared favourably with the method using serum‐soft agar (Yoshida 1972). With the new technique, many populations of encapsulated and unencapsulated strains were investigated. Of 1421 fresh isolates of Staph. aureus, 54 were encapsulated and among these 54·8% and 48·1% were mono‐ and polyvalent, respectively. Capsular‐type antigens A and B were found in 92·5% and 44·4% of strains respectively; capsular‐types C and D were found relatively infrequently. In the other group, of unencapsulated strains, capsular‐type antigen production was demonstrated in 125 out of 163 strains examined. Mono‐ and polyvalent capsular‐types (A and B antigen producing strains) comprised 77·6% and 22·4%. respectively. In these capsular‐types A and B were found in 54·4% and 62·4%, respectively: capsular‐type antigen C and D producing strains were again infrequent. These results indicate that a majority of ordinary Staph. aureus strains produce capsular‐type antigens although isolation of the encapsulated strains is infrequent.

An encapsulated strain of Staphylococcus epidermidis isolated from a human clinical specimen was demonstrated by electron microscopy. The outermost layer of the cell wall of these organisms probably consists mostly of polysaccharide.

S U M M A R YCompact-colony forming active substance (CCFAS), the material responsible for the compact colonies of Staphylococcus aureus observed in serum soft agar, was found to be an alkaline-stable, associated polysaccharide containing galactose, N-acetylglucosamine, ribitol, phosphorus and a small quantity of alanine. This substance, when extracted from strains unable to produce protein A and clumping factor, was able to absorb the serum-reacting factor whereas a teichoic acid preparation of one strain could not. The formation of CCFAS was unaffected by the age of the cells, whereas when staphylococci were cultured at alkaline pH, young cells produced more clumping factor than old ones. Both fibrinogen and its degradation products were capable of inducing compact colonies in a strain of S. aureus. The ability of human sera to interact in compact-colony formation was independent of the immunoglobulin content. Thus neither protein A, clumping factor, nor teichoic acid participate in the CCFAS reaction.

In the present study, a compact colonyforming active substance from Staphylococcus aureus strains was found to be alkali-stable and suspected to be of a polysaccharide nature located on the cell surface.Recently, Forsum et al [1] postulated that compact colony forms of S. aureus strains in serum-soft agar (SSA) were the result of protein A, which reacted with the IgG globulin. Yoshida et al [4,5], however, observed that the compact colonyforming activities (CCFA) of S. aureus strains which were enhanced by alkali were decreased when the medium was made acid. This phenomenon suggested that protein A, which is rather acid-stable, may not be directly related to the CCFA of S. aureus in SSA. Attempts were made, therefore, to obtain a substance exhibiting the CCFA from S. aureus strains.S. aureus strain PS84, which showed high CCFA as described elsewhere [4], and the Wood 46 strain of S. aureus, which was deficient in protein A as noted by Lind et al [2], were used. Strains PS84 and Wood 46, both of the compact type, were cultured at 37 C overnight in brain heart infusion (BHI, Difco) dialysate medium which was supplemented with a 1/10 volume of 0.3 of Tris-hydrochloride buffer (pH 8.4). Cells were harvested by centrifugation and resuspended in 0.03 M of a similar buffered solution. They were treated with a sonic oscillator at 10 kc for 5 min. Viable cell numbers of the organisms were not diminishRequests for reprints should be addressed to Dr. Kosaku Yoshida,

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